Drive for an adjustment device with a worm wheel having a globoid toothing with a cylindrical section

ABSTRACT

Drive for an adjustment device, comprising a worm wheel which has a globoid toothing with a central cylindrical section. The drive for an adjustment device, specifically, a seat adjustment device within a vehicle, has a spindle ( 5 ) and a gear mechanism ( 9 ) coupled thereto which has a drive worm ( 20 ) drivable by a motor ( 2 ). The drive worm ( 20 ) engages a worm wheel ( 40 ). The toothing of the worm wheel ( 40 ) has a central section with cylindrical toothing (Z), which section transitions on both sides into a globoid toothing (G) such that at least one complete annular surface remains on both ends of the worm wheel ( 40 ). A method according to the invention of fabricating this worm wheel provides for a cutter ( 60 ) which is moved vertically relative to the axis (A) of a worm wheel blank. Advantages: Elimination of thrust washers; improved acoustics, torque fluctuations and vibrations; simple fabrication; improved run-out of the end faces; bearing surfaces projecting beyond the addendum circle of the toothing possible; no ridging on the functional surfaces and thus elimination of a separate deburring procedure.

The invention relates to a drive for an adjustment device inside a vehicle, specifically, a seat adjustment device inside a vehicle as specified by the features of the preamble of claim 1, and to a preferred method of fabricating a worm wheel such as one employed in this type of drive.

A known drive for seat adjustment devices is described in EP 1 068 093 B 1. This drive is illustrated in that publication and in FIG. 1 here as well. As is shown, a holding plate 1 on which the seat of the vehicle is fastened is associated with a top rail 3. Fastening lugs 10 for a motor 2 are provided on holding plate 1, thereby enabling the motor to be rigidly connected to holding plate 1 and thus to top rail 3. Drive shafts 11 are located on both ends of motor 2. Flexible shafts may be employed for this purpose. These drive shafts 11 create the connection to a gear mechanism 9 which is described in detail in EP 1 068 093 B1. This gear mechanism 9 sits within a U-shaped retaining bracket 8 with fastening holes 7 by which gear mechanism 9 can be fastened to top rail 3.

Top rail 3 slides along a fixed bottom rail 4 fastened to the floor of the motor vehicle, either directly or via adjustment and/or bearing elements, not shown here.

In the functional position of top rail 3 and bottom rail 4, these components are held by their contact or support regions so as to create a cavity. A threaded spindle 5 is located within this cavity. This threaded spindle is accommodated between retaining brackets 6 which are fixed to bottom rail 4. To this end, retaining brackets 6 have fastening holes through which appropriate bolt connecting means or analogous fastening means project, and which are retained on bottom rail 4 by fastening holes 4 a. Spindle 5 itself is screwed on to retaining brackets 6 by appropriate fastening nuts.

FIG. 2 shows the details of gear mechanism 9. Gear mechanism 9 is composed of a drive worm 20 which is engaged through an outer toothing of worm wheel 30. Drive worm 20 is connected to motor 2 through drive shaft 11. Worm wheel 30 has an internal thread 32 which can engage threaded spindle 5. When motor 2 turns, it transmits its motion through drive shafts 11 to drive worm 20. This drive worm transmits its rotational motion to worm wheel 30. Since in this known drive system the threaded spindle is rotationally fixed to bottom rail 4, gear mechanism 9, and thus top rail 3 connected to the spindle together with the attached vehicle seat, must perform a longitudinal motion.

As is shown in FIG. 2, gear mechanism 9 including drive worm 20 and worm wheel 30 is located in a housing which is composed of four housing plates 14. This housing together with housing plates 14 is situated within the U-shaped recess of retaining bracket 8. Both drive worm 20 as well as worm wheel 30 have annular projections at their ends which are identified as reference numbers 21 and 31. These annular projections 21, 31 are supported within corresponding openings of housing plates 14. To accommodate them, the individual housing plates 14 have bearing holes or bearing bushings 14 a. For the axial run, so-called thrust washers 16 are seated on the above-mentioned annular projections 31 of worm wheel 30, while thrust washers 18 are seated on annular projections 21 of drive worm 20. These thrust washers 16, 18 are particularly necessary for worm wheel 30 since in conventional cylindrical toothings the ends of worm wheel 30 are interrupted. Thrust washers 21, 31 are needed to reduce wear.

This problematic aspect becomes particularly clear in the enlarged view of worm wheel 30 in FIG. 3. In FIG. 3, worm wheel 30 together with its cylindrical toothing 33 running helically relative to the axis A of worm wheel 30 is clearly seen. This cylindrical helical toothing 33 has helically shaped and continuous tooth crowns 34 and tooth roots 35.

The cylindrical helical toothing 33 of worm wheel 30 shown in FIG. 3 has the advantage that the toothing engagement with drive worm 20 is insensitive to any axial misalignment of the spindle nut caused by assembly, component tolerances, and wear of the individual components.

However, this cylindrical helical toothing 33 is problematic insofar as the ends of worm wheel 30 are interrupted—as is clearly evident in FIG. 3. This configuration thus results in the fact that tooth roots 35 of the toothing extend up to the end face at which annular projections 31 project. In order to preclude any damage to the bearing bushings contacting the interrupted end faces, while at the same time ensuring optimum support of worm wheel 30 in bearing bushings 14 a of housing plates 14, thrust washers 16 shown in FIG. 3 must be inserted over annular projections 31 and placed against the end faces of worm wheel 30. In order additionally to prevent these thrust washers 16 from sliding circumferentially, these washers as a rule have tabs 16 a which engage the toothing spaces of cylindrical helical toothing 33.

The use of these thrust washers 16 has various disadvantages, however. As additional required parts they increase the fabrication and assembly expense for this type of gear mechanism. In addition, thrust washers 16 produce undesirable noises. When these thrust washers 16 are used, specifically, rattling noises and frictional noises are produced which are caused by deviations in concentricity and shaft-center-distance tolerances. In addition, the axial play of the spindle nut within the housing is increased by the summation of individual tolerances.

The invention then takes the above as a starting point.

The goal of the invention is to improve the described known drive in such a way that fewer components are required, thereby reducing fabrication and assembly costs, while at the same time eliminating the noise problems on the basis of the new approach.

This goal is achieved by a drive which has the features of claim 1.

This type of drive is essentially distinguished by a worm wheel which is characterized by the fact that the toothing of the worm wheel as viewed in the axial direction of the worm wheel has a center section with cylindrical toothing, which section transitions on both sides into a globoid toothing such that at least one complete annular surface remains at the two ends of the worm wheel.

According to the invention, a worm wheel is proposed within the drive, which worm wheel has a globoid toothing with a cylindrical, preferably, central section. The invention combines the advantages of a cylindrical toothing, specifically, a cylindrical helical toothing, with the advantages of a conventional globoid toothing by an approach in which the globoid toothing is not provided within the central section of the worm wheel, but instead continues on both sides of a cylindrical section of the toothing. As a result, the disadvantages of a conventional globoid toothing are avoided in the worm wheel according to the invention.

The drive with a worm wheel designed according to the invention has the following advantages:

-   -   the toothing engagement is insensitive to any axial misalignment         of the spindle nut caused by assembly, tolerances of individual         components, and wear in the mounting of individual components;     -   the toothing operates in a significantly more favorable manner         as compared to a pure globoid toothing in terms of acoustics,         fluctuations in torque, and vibrations;     -   There is no interrupted end surface but instead a continuous         annular surface on the ends of the worm wheel, thereby         eliminating the need for thrust washers; and     -   a large segment of the end surfaces of the worm wheel can be         utilized as abutment surface.

Further modifications of the drive according to the invention are described in the subclaims which in turn reference claim 1.

A worm wheel as provided in the drive according to the invention is easily fabricated using the method specified in claim 14. Here the following methodological steps are employed:

-   a) providing a worm wheel blank; -   b) providing a rotating hobbing cutter (60) which is obliquely     offset by a predetermined angle relative to the axis (A) of the worm     wheel blank; -   c) Vertical insertion of cutter (60) orthogonally relative to     axis (A) into the worm wheel blank by a specified depth, and     longitudinal movement of cutter (60) by a specified travel (L) to     obtain the tooth space (45) of the toothing; -   d) Removal of cutter (60) from the generated tooth space (45).

In conventional approaches, cylindrical helical toothings are cut in such a way that the cutter is moved axially over the entire width of the toothing. The fabrication method according to the invention provides for radial cutting in which only the cylindrical section L is processed axially. As a result, worm wheels are able to be fabricated more quickly and in a more cost-effective manner.

The following discussion explains the invention in more detail in connection with additional figures based on various embodiments.

FIG. 1 shows the already described drive of prior art having a gear mechanism able to move along a spindle;

FIG. 2 is an exploded view of the already described gear mechanism of FIG. 1 having a drive worm and worm wheel;

FIG. 3 is an enlarged view of the already described worm wheel of FIG. 2 including the thrust washers;

FIG. 4 is a perspective view showing an example of a worm wheel such as that used in a drive according to the invention and preferably having a central, cylindrical helical toothing, from both sides of which a globoid toothing extends;

FIG. 5 is a side view of the worm wheel shown in FIG. 4;

FIG. 6 is a sectional view showing the worm wheel of FIGS. 5 and 6;

FIG. 7 is a perspective view showing the worm wheel of FIGS. 4 through 6 mounted on a spindle 5;

FIG. 8 is a graphic illustrating the fabrication of a worm wheel as shown in FIGS. 4 through 7 together with a cutter.

FIG. 9 shows another embodiment of the invention in which a toothed rack is provided.

Unless otherwise indicated, in the following figures identical reference notations indicate components with the same meaning.

FIG. 4 is a perspective view showing an embodiment of a worm wheel 40 according to the invention. FIG. 5 is a side view of the same worm wheel, while FIG. 6 shows a section through this worm wheel. FIG. 7 is a perspective view of this worm wheel mounted on spindle 5.

As viewed in its axial direction, worm wheel 40 has a circumferential section having cylindrical toothing Z which transitions on both sides into a globoid toothing G. At least one complete annular surface F remains at both ends of worm wheel 40. In order to ensure that this complete annular surface F remains at the axial ends, it is expedient to provide an edge region R on both the left and right axial sides of worm wheel 40 in which no toothing is cut.

Annular projections or flanges project from the two complete annular surfaces F.

As is especially evident in the perspective view of worm wheel 40 in FIG. 4 and the side view of FIG. 5, the region of the cylindrical toothing Z is centered relative to the longitudinal axis of worm wheel 40. Worm wheel 40 and cylindrical toothing Z, as well as the bordering globoid toothing G, are configured obliquely on the worm wheel—that is, toothing grooves are located obliquely relative to the axis of worm wheel 40. Relative to axis A, the obliquity has an offset angle of α.

The complete annular surface F at the ends of worm wheel 40 extends up to the outer diameter of worm wheel 40.

Cylindrical toothing Z extends, as viewed in the axial direction of worm wheel 40, over preferably the sum of the axial play, twice the axial misalignment, and twice the expected wear of the individual parts.

The tooth crown 43 in the region of cylindrical toothing Z relative to axis A of the worm wheel is depressed as compared to tooth crown 43 in the region of the globoid toothing of the worm wheel. The tooth bottom land in the tooth spaces 45 of the worm wheel has a central straight section from which circular-arc sections extend on both sides.

Worm wheel 40 also has an internal thread 47 which is made to engage spindle 5 of the drive.

Worm wheel 40 is preferably in the form of a milled metal part.

The fabrication of described worm wheel 40 is explained below in connection with FIG. 8. First, a worm wheel blank is provided. The desired tooth contour of worm wheel 40 is created using a rotating hobbing cutter 60. Here the hobbing cutter is obliquely offset by a predetermined angle relative to axis A of the worm wheel blank. The hobbing cutter is subsequently made to rotate and is inserted by a predetermined depth vertically to axis A of the worm wheel blank. The longitudinal movement proceeds by a predetermined travel L so as to obtain a tooth space 45 of the toothing. Cutter 60 is then removed from the generated tooth space 45.

This procedure is repeated for each tooth space to be generated. The above-mentioned angle by which the hobbing cutter is offset relative to axis A of the worm wheel blank is preferably between approximately 5° and 20°. This angle is plotted in FIG. 5.

The above-mentioned predetermined travel by which hobbing cutter 60 is moved longitudinally is between approximately 0.5 mm and 2 mm.

The fundamental advantage of employing a drive with a worm wheel 40 as described above consists in the fact that the otherwise-required conventional thrust washers can be eliminated. The drive is distinguished by improved acoustics, whereby fluctuations in torque and vibrations are essentially able to be avoided. In addition, the drive according to the invention is simpler to fabricate. Another feature achieved is an improved run-out of the end surfaces. Finally, bearing surfaces projecting beyond the addendum circle of the toothing can be provided. Another feature achieved by drive according to the invention is [the absence of]¹ ridging on the functional surfaces, and thus the friction surfaces, thereby eliminating a separate deburring procedure ¹ Translator's note: meaning corrected based on context.

FIG. 9 shows yet another embodiment of a drive according to the invention. In place of a spindle for the drive, a toothed rack 70 is now provided on which a worm 72 meshes. Preferably, worm wheel 40 is formed as an integrated component on worm 72, which worm wheel is driven by a drive worm 20.

Worm wheel 40 is preferably the worm wheel illustrated in FIGS. 4 through 7 which is connected in a rotationally fixed manner to worm 72 and coaxially aligned with this worm. Worm wheel 40 and worm 72 are preferably located on a common shaft.

LIST OF REFERENCE NOTATIONS

-   1 holding plate -   2 motor -   3 top rail, element -   4 bottom rail, element -   5 spindle -   6 bracket -   7 fastening holes -   8 retaining bracket -   9 gear mechanism -   10 fastening lugs -   11 drive shafts -   14 housing plates -   14 a bearing bushings -   16 thrust washers -   16 a tabs -   18 thrust washers -   20 drive worm -   21 annular projection -   30 worm wheel -   31 annular projection -   33 cylindrical helical toothing -   34 tooth crown -   35 tooth root -   40 worm wheel -   41 annular projection -   43 tooth crown -   45 tooth root -   47 interior thread -   60 cutter -   70 toothed rack -   72 worm -   A axis -   F annular surface -   G globoid toothing -   L travel -   Z cylindrical toothing -   R edge region -   T insertion depth 

1. Drive for an adjustment device within a vehicle, comprising a spindle (5) which is attached to one of two elements (3, 4) that are adjustable relative to each other, and comprising a gear mechanism (9) drivable by a motor (2), which gear mechanism is located on the second element (4), wherein the gear mechanism (9) has a drive worm (20) drivable by the motor (2), the drive worm engaging a worm wheel (40) coupled to the spindle (5), where the toothing of the worm wheel (40) has, as viewed in the axial direction of the worm wheel (9), a circumferential section with cylindrical toothing (z), which section transitions on both sides into a globoid toothing (g) such that at least one complete annular surface (f) remains on both ends of the worm wheel (40).
 2. Drive according to claim 1, where the section with the cylindrical toothing is centered relative to the longitudinal axis of the worm wheel.
 3. Drive according to claims 1, where the worm wheel (9) has the cylindrical toothing (Z) and bordering globoid toothing (G) in the form of toothing grooves oriented obliquely to the axis (A) of the worm wheel (9).
 4. Drive according to claims 1, where the annular surface (F) on the ends of the worm wheel (40) extends to the outer diameter of the worm wheel (40).
 5. Drive according to claim 1, where the complete annular surface (F) on the ends of the worm wheel (40) has a height which lies between the tooth root (45) and tooth crown (43) of the toothing of the worm wheel (40).
 6. Drive according to claim 1, where the annular surface (F) on the ends of the worm wheel (40) is at least approximately as large as the bearing bushings (14 a) of a housing (14) accommodating the gear mechanism (9).
 7. Drive according to claim 1, where the cylindrical toothing (Z), as viewed in the axial direction of the worm wheel (40), extends axially over preferably the sum of the axial play, twice the axial misalignment, and twice the expected wear of the individual parts.
 8. Drive according to claim 1, where the tooth crown (43) is depressed in the region of the cylindrical toothing (Z)—relative to the axis (A) of the worm wheel (40)—as compared to the tooth crown (43) in the region of the globoid toothing (G) of the worm wheel (40).
 9. Drive according to claim 1, where the tooth bottom land in the tooth spaces (45) has a central straight section from which circular-arc sections extend on both sides.
 10. Drive according to claim 1 where the worm wheel (40) has an internal thread (47) which engages the spindle (5).
 11. Drive according to claim 1 where the spindle (5) is fixed and the worm wheel (40) is located rotatably on the spindle (5).
 12. Drive according to claim 1, where the worm wheel (40) is in the form of a milled metal part.
 13. Drive according to claim 1, where the worm wheel (40) has on both ends annular projections (41) formed as integrated components of the worm.
 14. Drive according to claim 1, where the adjustment device is a seat adjustment device for a motor vehicle.
 15. Method of fabricating a worm wheel (40), comprising: a) providing a worm wheel blank; b) providing a rotating hobbing cutter (60) which is obliquely offset by a predetermined angle relative to an axis (A) of the worm wheel blank; c) vertically inserting the cutter (60) orthogonally relative to the axis (A) into the worm wheel blank by a specified depth, and longitudinal movement of the cutter (60) by a specified travel (L) to obtain a tooth space (45) of the toothing; d) removing of the cutter (60) from the generated tooth space (45).
 16. Method according to claim 15, angle α is between approximately 5° and 20°.
 17. Method according to claim 16, where the specified travel (L) is between approximately 0.5 mm and approximately 2 mM.
 18. Method according to claim 17, where a hobbing cutter is employed as the cutter (60). 